As illustrated in FIG. 7, the steering apparatus of an automobile is constructed such that it applies a steering angle to the front wheels by transmitting the rotation of a steering wheel 1 to an input shaft 3 of a steering gear unit 2, and pushing or pulling a pair of left and right tie rods 4 as the input shaft 3 rotates. The steering wheel 1 is supported by and fastened to the rear end section of a steering shaft 5, and with the steering shaft 5 passed in the axial direction through a cylindrical shaped steering column 6, the steering shaft 5 is supported by this steering column 6 such that it can rotate freely. The front end section of the steering shaft 5 is connected to the rear end section of an intermediate shaft 8 via a universal joint 7, and the front end section of the intermediate shaft 8 is connected to the input shaft 3 via a separate universal joint 9. The intermediate shaft 8 is constructed such that it is capable of transmitting torque, and such that its entire length can be contracted by an impact load. During a collision accident, regardless of backward displacement of the steering gear unit 2, due to contraction of the intermediate shaft 8, the steering wheel 1 is prevented from displacing toward the rear with the steering shaft 5 and thus from being pressed up against the body of the driver.
During a collision accident, it is required for this kind of steering wheel apparatus for an automobile to have construction that causes the steering wheel 1 to displace in the forward direction as it absorbs impact energy so as to protect the driver. In other words, during a collision accident, after a primary collision of an automobile with another automobile, a secondary collision occurs in which the body of the driver hits the steering wheel 1. Technology has been conventionally employed in which the impact applied to the body of the driver during this secondary collision is lessened by supporting the steering column 6 that supports the steering wheel 1 with respect to the vehicle body so that the steering column 6 drops away toward the front due to the impact load of this secondary collision, and by providing an energy absorbing member, which absorbs an impact load by deforming plastically, between a portion that displaces in the forward direction together with the steering column 6 and the vehicle body.
FIGS. 8 to 11 illustrate an example of an automobile steering apparatus that comprises this kind of impact absorbing function. This steering apparatus comprises a steering column 6a, a bracket 10 on the column side, a pair of left and right held wall sections 11 that are provided on the steering column 6a side, and a bracket 12 on the vehicle body side. A steering shaft 5a is supported on the inner-diameter side of the steering column 6a by way of a rolling bearing that is capable of supporting a radial load and a thrust load such that the steering shaft 5a can only rotate freely. A housing 14 for installing the component members of an electric power steering apparatus such as an electric motor 13 (see FIG. 7) and reduction gear, is connected and fastened to the front end section of the steering column 6a. 
Moreover, the bracket 10 on the column side is connected to and supported by the bracket 12 on the vehicle body side such that the bracket 10 can displace in the forward direction and detach due to an impact load that is applied during a secondary collision. The bracket 10 on the column side is formed by connecting and fastening together a top plate 15 and a pair of left and right side plates 16a, 16b, which are metal plates having sufficient strength and rigidity such as steel plate, by a method such as welding. Both end sections in the width direction of the top plate 15 function as installation plate sections 17 for connecting the bracket 10 on the column side to and supporting it by the bracket 12 on the vehicle body side. Cut out sections 18 as illustrated in FIG. 11 are opened at the rear end edge of these installation plate sections 17 in the center section in the width direction of these installation plate sections 17, and capsules 19 are respectively mounted in these cut out sections 18.
These capsules 19 are made of a material that slides easily over the metal plate of the top plate 15 such as a synthetic resin or a soft metal including an aluminum alloy. The capsules 19, in the normal state do not come out from the cut out sections 18, however when a large impact load is applied to the bracket 10 on the column side in the forward direction, members for locking the capsules 19 inside the cut out sections 18 shear, and the capsules 19 come out from the cut out sections 18. More specifically, shear pins span between the concave sections 20 and small through holes 21 that are formed in the inner circumferential edge or surrounding portion around the cut out sections 18 in the installation plate sections 17, and other small through holes 22 that are formed in the capsules 19. These shear pins are formed using a material that can shear under an impact load such as a synthetic resin or a soft metal, and with at least part of each of the pins being tightly pressure fitted inside the small through 21, 22, the pins span between the installation plate sections 17 and the capsules 19, and these installation plate sections 17 support these capsules 19.
Through holes 23 are formed in the center section of the capsules 19 for inserting bolts or studs for connecting the bracket 10 on the column side to and supporting the bracket 10 by the bracket 12 on the vehicle side. In order to connect the bracket 10 on the column side to and supporting the bracket 10 by the bracket 12 on the vehicle side, the bolts are inserted from bottom to top through the through holes 23 in the capsules 19, and screwed into nuts 24 that are supported by and fastened to the bracket 12 on the vehicle side by welding or the like, and tightened. This bracket 12 on the vehicle side is fastened to the vehicle body beforehand, so by tightening the bolts, the bracket 10 on the column side is connected to and supported by the vehicle body so that it can only drop toward the front when a large impact load is applied in the forward direction.
The steering column 6a is supported between the side plates 16a, 16b of the bracket 10 on the column side. The steering column 6a is supported to the bracket 10 on the column side such that the steering column 6a is displaced in the forward direction together with the bracket 10 on the column side, and the steering shaft 5a is supported by the steering column 6a such that the steering shaft 5a can only rotate freely. Therefore, in a secondary collision, when an impact load is applied in the forward direction to the steering wheel 1 that is fastened to the steering shaft 5a, the steering column 6a disengages from the bracket 12 on the column side, and displaces in the forward direction together with the steering wheel 1.
When a large impact load in the forward direction is applied from the steering wheel 1 to the bracket 10 on the column side during a secondary collision, the shear pins that span between the capsules 19 and the installation plate sections 17 shear off, and the capsules 19 come out from the cut out sections 18, and the bracket 10 on the column side displaces in the forward direction. As a result, the steering wheel 1 also displaces in the forward direction, which lessens the impact applied to the body of the driver that hits against the steering wheel 1.
From the aspect of protecting the driver, when the steering wheel 1 is caused to displace in the forward direction during a secondary collision, it is further desired that a mechanism be provided that absorbs the impact energy that is applied to the steering wheel 1 from the body of the driver. For example, even in the construction illustrated in FIG. 7 to FIG. 11, a friction force acts on the areas of contact between the outside surfaces of the held wall sections 11 and the inside surfaces of the side plates 16a, 16b, and a friction force acts on the area of contact between the inner circumferential surface on the front section of the outer column and the outer circumferential surface on the rear end of the inner column, and this becomes resistance to the displacement of the steering wheel 1 in the forward direction, and contributes to absorbing impact energy.
Furthermore, construction is disclosed in Patent Literatures 1 to 3, wherein an energy absorbing member, which allows the steering column to displace in the forward direction while plastically deforming, is supported by the vehicle body and is located between a portion that displaces in the forward direction during a secondary collision and a portion that does not displace in the forward direction during a secondary collision. FIGS. 12 to 14 illustrate a first example of conventional construction as disclosed in Patent Literature 1 in which an energy absorbing member is installed. In the case of this first example of conventional construction, a metal plate that is capable of plastic deformation, such as mild steel plate, and that is bent into the shape illustrated in FIG. 13 is used as the energy absorbing member 25. The rear section of the energy absorbing member 25 is connected to the bracket 12a on the vehicle side together with the pair of left and right installation plate sections 17a that are provided on the bracket 10 on the column side by a bolt 26. U-shaped cut out sections, for example, are formed on the installation plate sections 17a with opened at the rear end edge thereof, and the bolt 26 is inserted though the cut out sections. The front section of the energy absorbing member 25 is bent back in a U shape, and as illustrated in FIG. 12, the edge of the tip end is fitted with part of the installation plate sections 17a, such that during a secondary collision, this edge on the tip end displaces in the forward direction together with the bracket 10a on the column side.
As illustrated in FIG. 14, when a secondary collision occurs, the bracket 10a on the column side displaces in the forward direction while the bolt 26 comes out from the cut out section toward the rear. However, the rear section of the energy absorbing member 25 is supported by the bolt 26, and remains on the portion of the bracket 12a in the vehicle body side. Therefore, the energy absorbing member 25 elongates due to plastic deformation from the state illustrated in FIG. 12 to the state illustrated in FIG. 14. Due to this elongation, impact energy that is applied to the steering wheel 1 during a secondary collision is absorbed, which lessens the impact that is applied to the body of the driver that hit against the steering wheel. Patent Literature 3 also discloses construction similar to that disclosed in Patent Literature 1, wherein an energy absorbing member made using a metal plate is installed.
FIGS. 15 to 17 illustrates a second example of conventional construction as disclosed in Patent Literature 2, wherein an energy absorbing member is installed. In the case of this second example of conventional construction, wires made of metal that is capable of plastic deformation such as mild steel and that are bent into the shapes illustrated in FIG. 16 are used as a pair of energy absorbing members 25a. The bent back base section 27 of the energy absorbing member 25a is fastened to the rear side of the capsule 19a which is supported by the bracket on the vehicle side and does not displace in the forward direction even during a secondary collision. On the other hand, the bent back section 28 on the front end side of the energy absorbing member 25a faces the front end edge of the installation plate section 17b of the bracket 10b on the column side. Furthermore, the straight section 29 that is continuous from the bent back section 28 on the front end side toward both end sections of the wire member passes through a through hole 31 that is formed in the flat plate section 30 of the bracket 10b on the column side is caused to protrude to the rear further than the flat plate section 30.
When a secondary collision occurs, as the steering column 6b to which the bracket 10b on the column side is fastened displaces in the forward direction, the front end edge of the installation plate section 17b engages with and moves the bent back section 28 on the front end of the energy absorbing member 25a. The straight section 29 comes out from the through hole 31, and the bent back section 28 on the front end side is caused to move toward both end sections of the wire. The movement of these bent back sections 28 on the front end sides is performed as plastic deformation of these wire members, so this movement absorbs the impact energy that is applied to the steering wheel during a secondary collision, which lessens the impact applied to the body of the driver that hit against the steering wheel.